fix(agent): 对齐 EventType.ALL 的文档与流式行为

[guslegend0510]

做了什么

• 明确 EventType.ALL 和 StreamOptions#getEventTypes() 实际会包含 AGENT_RESULT
• 同步更新英文/中文流式文档，和真实行为保持一致
• 补充回归测试，验证 EventType.ALL 会流式输出 AGENT_RESULT

原因

• Issue EventTypes针对ALL的注释和实际代码实现逻辑不相符 #1439 指出注释/文档与实现不一致
• 这次只统一说明与测试，不修改运行时逻辑

验证

• mvn -pl agentscope-core spotless:apply
• mvn -pl agentscope-core -Dtest=StreamOptionsTest test

Fixes #1439

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!